Figure 3—Here are the port A assignments. With just 13 I/O pins available, allocation is critical. b—With the port B pin assignments, just three pins are needed for the A/D conversion, but five are required for the LCD controller.

may96f3.gif (2543 bytes)

ac_pwr Analog input Analog AC power input (PIC16C71 only)

9V_sense Analog input Analog 9-V battery sense (PIC16C71 only)

ay_arr_out Arrow segment pin of LCD

ay_bp LCD backplane input pin

may96f3b.gif (2512 bytes)

mode_sw Active low Indicates mode switch depressed

res_sw Active low Indicates reset (or zero) switch depressed

ad_cs Active low Chip select to ADC0831

ad_clk Falling edge Data valid out of ADC on falling edge

ad_dat Data output of ADC0831

ay_dat Data input to AY0438 LCD driver chip

ay_clk Falling edge Clock input to AY0438, data is clocked into AY0438 on falling edge

ay_ld Rising edge Data is transferred from AY0438 shift register to output latches